1. Field of the Invention
The invention relates to a matrix pin print head with adjustable print pin guide, where a print pin drive device group and a pin print guide device group, disposed toward a print counter support, are provided with a casing guiding the print pins, and where an electric lifting magnet for a magnet core is disposed in the region of the print pin guide device group, where the magnet core, together with a pin guide carrier, forms an adjustable magnetic discontinuity air gap, and where the pin guide carrier is movable back and forth between two fixedly adjustable positions.
2. Brief Description of the Background of the Invention Including Prior Art
Such matrix pin print heads with adjustable print pin guide serve to generate various stages of letter-quality printing such as, for example, the generating of near-letter-quality printing as well as letter-quality printing. In this context, after one print pass, i.e. after the running through of a print line in a second print pass or in a return pass following the first print pass, the print pin guide is readjusted by less than a pin distance of about 0.3 mm, whereby the pin distance gaps are filled by further print points/dots. The adjustment of the print pin guide therefore requires a very high degree of precision between two fixed positions of impact, where the print pins are guided in a pin guide stone, which is produced from a similar material as the bearing stones for small watches.
It is known from German patent applications Laid Open DE-OS 3,412,854, DE-OS 3,412,856, DE-OS 3,403,795, DE-OS 3,412,855, and U.S. Pat. No. 4,640,633 that in case of very long print pins, which require a very long casing guiding the print pins, an electric lifting magnet can be disposed at the inside or at the outside of this casing, which magnet runs about along the print pins and about parallel to these print pins.
In this case, the print pin guide and this pin guide stone are disposed at a relatively long lever arm which, in most cases, is tiltably supported around a hinge in the region of the print pin drive device group. The motion of the pin guide stone on an arc with the radius equal to the length of the lever arm is in fact disadvantageous, because the chord height of the arc becomes noticeable in a certain adjustment region. However, up to now, this disadvantage has been considered as permissible. As far as that is concerned, such adjustable print pin guides have worked in thousands of matrix pin print heads.
Very long print pins, however, have in the meantime shown to be disadvantageous for the following reasons. The larger mass of longer print pins interferes with the print frequency, i.e. a smaller mass allows for an increase in the print frequency. The desired shorter acceleration times can be achieved with a smaller mass. Shorter print pins mean however also a shorter casing of the print pin guide device group. However, a shorter lever arm is associated with a shorter print pin, at which lever arm the pin guide carrier is attached. The shorter lever arm means a decrease of the radius, i.e. a stronger curvature bend of the arc and a shorter radius of curvature of the arc, on which arc the pin guide stone can be moved back and forth. However, it has to be taken into consideration simultaneously that shorter print pins are stiffer than longer print pins and it is therefore more difficult to bend such print pins, which in turn means that a larger drive force has to be furnished by the print pin drive device group because of increased friction in the guide planes.